add external data type support for DataSetJSONMarshaller

[StephenOTT]

when serializing datasets using org.dashbuilder.dataset.json.DataSetJSONMarshaller the generated data set is not supported by default?

I seem to have to use a custom expression to format the results into a {columns:[], values:[]} result within the expression config of the dashboard.

If this is accurate, it would be great if we could create support similar to prom and https://github.com/kiegroup/kie-tools/pull/1825

[ederign]

@StephenOTT, currently, we are short on people to address more general questions and fix Dashbuilder's general issues in the community. So, it may take longer to get back to you on this. Sorry about that.

Dashbuilder as a library is still part of our Serverless Workflow Dashboards/Monitoring.